1. Field of the Invention
This invention relates to matrix drive display electronic timepieces and more particularly to a matrix drive display electronic timepiece which can reliably deliver a pitch measuring signal.
2. Description of the Prior Art
An electronic timepiece operative to count a frequency of a crystal oscillator and digitally display the numerical values thus counted as the time with the aid of an electronic-optical display of a liquid crystal display device or the like having a selective pattern of numerals has been well known. It has also been well known that a display pattern drive for an electronic-optical display device such as a liquid crystal display device or the like is composed of a so-called static drive and matrix drive. The matrix drive is also called as a dynamic drive. In the static drive, one of a pair of transparent electrodes for respective segments between which is sandwiched a liquid crystal layer of a liquid crystal cell is integrated into one common electrode to which is applied a rectangular voltage wave having a given frequency of several tens of Hz, while the other transparent electrode constitutes a display pattern connected to a terminal. To non-display segments is applied a voltage wave which is the same in amplitude and phase as the voltage wave applied to the common electrode and to display segments is applied a voltage wave which is opposite in phase to the voltage wave applied to the common electrode. As a result, only those liquid crystal substrate layers which correspond to the display segments are brought into a drive electric field.
In the matrix drive, one of the pair of transparent electrodes for respective segments is not made integral into one common electrode, but is divided into several electrodes which are called column electrodes. Segment electrodes constituting display patterns are not separated from each other and that segment electrode which corresponds to each column electrode is assembled together into a group of electrodes which are called line electrodes.
The voltage wave applied to the column electrode is so shaped that only those segment groups which belong to one column are simultaneously displayed and that this display condition is revealed at each column at a high cycle in a time separation manner.
The voltage wave applied to the line electrodes is made different in accordance with those elctrodes which are disposed on the column electrodes and which are to be driven.
The liquid crystal layer functions in substantially dependence with the effective value (root mean square value) of a driving voltage difference wave form. This behavior of the liquid crystal substance is utilized so that a effective voltage value larger than a threshold value required for displaying segments is selectively applied to that liquid crystal portion which corresponds to the segments to be displayed and so that a effective voltage value smaller than the threshold value is selectively applied to that liquid crystal portion which corresponds to the segments to be extinguished. In general, the voltage wave form applied to the column or line electrodes is a complex stepshaped waveform which is composed of a combination of several predetermined voltage levels.
A drive means for a liquid crystal display electronic wrist watch, which has heretofore been used in practice, comprises an electric source circuit and a drive circuit which is simple in construction and which is not required to be operated in a highly stable manner, and as a result, makes use of the static drive which can easily select the liquid crystal substance and which permits allowances for the precision required for working the liquid crystal display cell.
The matrix drive provides the important advantage that the total number of electrode terminals led out of the display device is about one-half that of the static drive and hence the connection thereof to the drive circuit becomes simplified, thereby reducing the manufacturing cost of the timepiece, improving the reliability of operation and rendering it possible to display a letter composed of many segments, and characters having a number of figures. As a result, if the technical level of manufacturing the circuits and liquid crystal cell becomes high, the matrix drive would be used in practice in near future. It has been the common practice to use the matrix drive for the liquid crystal of an electronic table computer.
Even in the electronic wrist watch, it is necessary to check its pitch at any desired time for the maintenance purposes. In this case, it is preferable to deliver a pitch signal without opening a cover of the watch. In conventional liquid crystal display time-pieces, provision is made of a metal plate adjacent to a viewing crystal provided at a display surface and a slight voltage change induced by the static drive is amplified so as to prepare a pitch signal.
On the contrary, in the matrix drive, if use is made of the above mentioned technique, a pitch measuring instrument becomes erroneous in operation owing to unstable detection levels and low sensitivity caused by complex voltage wave forms for transferring a number of voltage levels at a high speed, and by a small number of segments which are the same in voltage wave form and the like.